The surprisingly deep analogy between compact Riemann surfaces and compact metric graphs lies at the heart of many recent developments in tropical geometry. In this talk I will give a short introduction to tropical geometry via this analogy focusing on linear systems. I will explain the process of tropicalization and discuss the realizability problem as well as some its partial solutions (and why a general solution is provably out or reach). This talk is based on joint work with Madeline Brandt, Martin Moeller and Annette Werner, as well as Dmitry Zakharov.